This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Currently, mobile communication technologies are evolving to very high frequencies, larger carrier bandwidths, very high data rates and multiple heterogeneous layers. The future mobile networks are likely to be a combination of evolved 3G technologies, 4G technologies and emerging or substantially new components such as Ultra-Density Network (“UDN”), which is also referred to as mmW-radio access technology (“RAT”). Due to the increasing demand to enhance wireless capacity and the lack of availability of spectrum in the lower frequency range (e.g., 800 MHz˜3 GHz), the use of frequencies in 10 GHz range is being investigated and higher frequency bands, for instance, in the range of 30 GHz, 60 GHz and 98 GHz for future mobile networks are also explored. At these high frequency bands, a very large bandwidth of spectrum could be obtained. This means that both operating frequency and bandwidth for the future mobile networks are expected to be much higher than those used in the legacy mobile networks. However, due to large signal attenuation with respect to path loss, the network operating over such high frequencies is supposed to cover small areas with densely deployed radio access nodes (“ANs”) or access points (“APs”), such as base stations, thereby providing sufficient coverage for indoor/hot areas.
The mmW RAT as mentioned above is now being investigated to use a plenty of very high frequency bands. In order to conquer or compensate the large attenuation due to the utilization of the very high frequency bands, high gain beamforming is inevitable and may be mandatory. To this end, given relatively small wavelengths, more antenna elements with the same size may be integrated into an antenna panel, thereby making it possible to reach higher beamforming gains. However, when there are several tens or hundreds of antenna elements, it would engender unacceptable costs if one RF chain is arranged for each antenna element. In this case, multiple antenna elements sharing one RF chain and analog phase adjustment are applied for each antenna in order to adjust the beam direction and maximize the beamforming gains. With respect to the narrow transmitter (“TX”) beams, the transmission of the downlink signals, for example, such as reference signals or beacon signals, should be carefully steered to enable AN discover area. In addition, the beamforming training should be carried out so as to maximize the beamforming gains during the service provision. The beamforming training herein may include both uplink and downlink beamforming training or both transmitter training and receiver training. The steered downlink transmission may increase the link gain while the beamforming training may maximize the beamforming gain of the service radio link.
For the downlink transmission detection, both the transmitter and receiver (“RX”) beamforming gains may be expected. In particular, the transmitter beamforming is already enabled at the AN side and the terminal devices, such as the user equipments (“UEs”) are able to blindly detect the downlink messages (e.g., beacon messages) using the receiver beamforming.
For the uplink control messages such as those transmitted on the physical random channel (“PRACH”), receiver beamforming gain may be expectable. However, the transmitter beamforming gain of the PRACH is hard to be fully achieved due to absence of beamforming training performed before PRACH transmission. In particular, the mobile terminals may only derive the uplink precoding matrix based on the angle of arrival (AoA) of the best beacon beam relying on the reciprocity. However, this is not so concrete since the downlink radio link and uplink radio link are served by different transmitter and receiver chains although they share the same air media. If a narrow receiver beam is used for PRACH reception and/or transmission, even relatively small direction deviation from the desired direction could clearly reduce the link gain of PRACH reception at the AN side. If signals on PRACH is transmitted with wide beams, the link gains for the PRACH transmission could be much smaller than the downlink beacon signal because the transmitter beamforming gain cannot be sufficiently achieved, which imposes a problem on the PRACH coverage. Moreover, in practice, a single AN network may be accessed by various terminal devices with different capabilities, for example, such as, different power classes, different numbers of antenna elements, different antenna manufacturing, different schemes to process beamforming, various mobility and interference situations, etc.
In view of the above, how to match the coverage of the downlink signal with that of the uplink signal so as to achieve better wireless transmission and reception should be taken into account, especially in the wireless communication of the high frequency bands.